Question

I have a class:

class X {
  vector<shared_ptr<T>> v_;

 public:
  vector<shared_ptr<const T>> getTs() { return v_; }
};

It has a vector of shared_ptr of type T. For some reason, it needs to expose a method to return this vector. However, I don’t want the content of the vector to be modified, neither are the objects being pointed to. So I need to return a vector of shared_ptr<const T>.

My question is, is there any efficient way to achieve this? If I simply return it, it works, but it needs to reconstruct a vector, which is kind of expensive.

Thanks.

Answer 1

You can not do that directly – but you can define “views” on your container that let you do something very similar, if you want to make sure that your pointees are const:

boost::any_range<
  std::shared_ptr<const int>,
  boost::random_access_traversal_tag,
  std::shared_ptr<const int>,
  std::ptrdiff_t
> foo(std::vector<std::shared_ptr<int>>& v)
{
  return v;
}

A simple transform iterator adapter / transformed range might do the trick as well, I just used this to illustrate the point.